A great variety of polymers have been utilized for modifying the properties of lubricating oils. Not only do these polymers increase the viscosity of the oil, but certain polymers will improve the viscosity index of the composition. This is becoming increasingly important as industry, particularly the automotive industry, makes more stringent demands for oils which will perform satisfactorily at both low and high temperature conditions. While many polymers, such as the polymethacrylates, are satisfactory for the production of multigrade oils such as 10W/30 and the like, the low temperature properties and shear stability properties of oils containing these polymers limit the utility of these polymers for multigrade oils having a wider applicability.
Hydrogenated polymers which have been used in the past include hydrogenated diene polymers, selectively hydrogenated random copolymers, and both selectively and completely hydrogenated block copolymers. These have been described at times as "substantially completely hydrogenated polymers." By this, the art has made the assumption that the hydrogenation of a defined class of double bonds such as olefinic double bonds was "essentially complete" when, actually less than 98% of the double bonds were reduced. With further investigation, however, it is becoming more evident that insofar as high levels of stability are concerned, this incomplete olefinic saturation is not completely satisfactory, especially under the influence of oxygen, high temperature and shear.